The present invention relates generally to intersatellite communication, and more particularly to a high power optical combiner that allows for high data rates necessary for intersatellite communication.
Double-hop transmission is a condition where two ground stations may indirectly communicate with each other with the assistance of an intermediate ground station. A double-hop satellite link typically arises where two ground stations are sufficiently remote from each other that they do not have a direct link to the same satellite. As a result, the signal travels through space twice.
In particular, a transmitting ground station sends the signal through a first satellite to the intermediate ground station. Then, the intermediate ground station sends the signal through a second satellite to a recipient ground station.
Several disadvantages of double-hop satellite links are known. Double-hop satellite links double the satellite delay normally attributed to direct satellite links. Also, double-hop transmission is known for producing an inconvenient delay in sound for video conferencing. In this regard, a user may see parts of a video transmission before the associated sound is played. Furthermore, service costs may be doubled and security problems may arise with the use of an additional satellite and an additional ground station.
One proposed solution discloses serially cascading amplifiers for providing the necessary power for intersatellite communication. As is known in the art, a significant amount of optical power, e.g. about 4 Watts, is required for intersatellite communication. Intersatellite communication would eliminate the need to communicate through an intermediate ground station thereby alleviating the problems associated with double-hop transmission.
However, serially cascading stages can only be effective for a relatively small number of stages and moderate output powers. As more stages are added, amplifier spontaneous emission (ASE) is also amplified. This high power noise depletes the population inversion and consequently decreases the overall efficiency of the amplifier. In other words, the additional stages may even reduce power of the output signal. Also, the addition of stages typically increases the weight and power consumption of the amplifier.
Therefore, a need exists for an apparatus that provides sufficient optical power for intersatellite communication without increasing ASE.
It is therefore an object of the present invention to provide a high power optical combiner for enabling the transmission of substantial amounts of electronic data at high data rates.
In accordance with the above and other objects of the present invention, a high power optical combiner is provided. In one embodiment, the high power optical combiner includes a splitter having a splitter input and two splitter outputs. The splitter input receives an optical signal which the splitter divides into two sub-signals. The splitter outputs have coupled thereto a reference arm and a dither arm. Both arms transmit the sub-signals in parallel and have integrated therein an amplifier for amplifying the sub-signals in parallel. Furthermore, each arm is connected to a coupler input of a combining coupler. The combining coupler constructively combines the amplified sub-signals to produce a primary amplified signal that is transmitted through the coupler output.
The coupler output has a dither tap coupler attached thereto for drawing a secondary amplified signal from the primary amplified signal. The secondary amplified signal is coupled to a phase controller and a polarization controller, both of which are also coupled to the dither arm between the splitter and the amplifier. The phase controller and the polarization controller respectively adjust the phase and the polarization of the sub-signal in the dither arm so as to allow for efficient combination of the amplified sub-signals.
One advantage of the invention is that sufficient power can be provided to an optical signal for allowing intersatellite communication.
Another advantage of the present invention is that amplified spontaneous emission or xe2x80x9cnoisexe2x80x9d is kept relatively low despite substantial amplification of the optical signal.
Still another advantage of the invention is that a relatively low power supply is required to operate the invention.
Yet another advantage of the invention is that the high power optical combiner is relatively light weight thereby increasing efficient manufacture of satellites, as well as various other device employing high power optical combiners.
Another advantage of the invention is that semiconductor lasers may be employed as an amplifier and a phase adjustment element. Semiconductor lasers are of a mature technology and therefore have high reliability and efficiency.